1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to transceivers that operate in such systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to an antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
Many wireless transceivers are able to support multiple communication standards, which may be in the same frequency band or in different frequency bands. For example, a wireless transceiver may support Bluetooth communications for a personal area network and IEEE 802.11 communications for a Wireless Local Area Network (WLAN). In this example, the IEEE 802.11 communications and the Bluetooth communications may be within the same frequency band (e.g., 2.4 GHz for IEEE 802.11b, g, etc.). Alternatively, the IEEE 802.11 communications may be in a different frequency band (e.g., 5 GHz) than the Bluetooth communications (e.g., 2.4 GHz). For Bluetooth communications and IEEE 802.11b, (g), etc. communications there are interactive protocols that appear to the user as simultaneous implementation, but is actually a shared serial implementation.
Regardless of which standard a transceiver is currently support, if the standard requires full duplex communications, the transceiver must include a technique to minimize the adverse affects of transmissions of RF signals (i.e., blocker signals) upon receptions of RF signals. Many standards address this by providing a transmission frequency and a reception frequency (e.g., 1920-1980 MHz for uplink WCDMA communications and 2110-2170 MHz for downlink WCDMA communications). While standardized transmission and reception frequencies eliminate direct overlap, the transmitted signal still adversely affects the received signal when the signal strength difference is substantial (e.g., 40 dBm or more).
To further reduce the blocker signal within the receiver section, the receiver section includes an RF blocking circuit, a duplexer, and/or baseband circuitry to filter out the blocker signal. For a transceiver that supports multiple standards in multiple frequency bands, multiple RF blocking circuits, multiple duplexers, and/or multiple baseband circuits may be required to reduce the adverse affects of the blocker signal on the received RF signal. Note that a cordless phone, which operates in a single standard, may use one frequency for the transmit path and another frequency for the receive path to obtain a reduction in transmitter interference.
Therefore, a need exists for an improved technique for reducing the adverse affects of a blocker signal on the received RF signal in a multiple frequency band multiple standard transceiver.